Hamada, H.; Takamura, A.; Hasegawa, T.; WEN, W.; Itaguchi, Y.; Kikuchi, K.; Yozu, A.; Ota, J.; Nakamura, A.; Fujita, H.; Suzuki, K.; Yamashita, A.; An, Q.

Background: Balance instability is a major contributor to disability and falls in people with Parkinson's disease (PwP) and is often insufficiently explained by motor impairment alone. Altered awareness of motor control has been suggested to contribute to sensorimotor dysfunction in PwP, but its relationship with balance performance is poorly understood. Objective: To determine whether awareness of balance control, assessed using a control detection task (CDT), differs between healthy controls (HC) and PwP, and whether CDT performance is associated with balance-related measures. Methods: Healthy older adults (n=20) and PwP (n=22) performed a standing version of the CDT based on center-of-pressure (COP) control, using a force plate. CDT accuracy was used as the primary outcome measure. Static balance during quiet standing was assessed using the COP trajectory length and rectangular area. Dynamic standing balance was assessed using the Index of Postural Stability (IPS). Group differences were examined by independent-samples t-tests. Correlations between CDT accuracy and balance measures were analyzed. Results: The PwP group showed significantly lower CDT accuracy. Higher CDT accuracy was associated with better static balance in the HC group and the combined sample, and with higher IPS primarily in the PwP group. Conclusions: Motor awareness during postural tasks is altered in PwP and is associated with balance control. These findings suggest that balance instability in Parkinson's disease may involve altered balance-related action-outcome monitoring in addition to motor dysfunction.